The present invention relates to a data transmission system having a high-speed transmission line for coupling a plurality of data transmission apparatuses and terminals connected to these data transmission apparatuses, thereby performing communication between the terminals in accordance with high-speed transmission procedures.
A high-speed data way system is known as a data transmission system of this type wherein a plurality of data transmission apparatuses (nodes or data transmission stations; to be referred to as stations hereinafter) are looped together by a high-speed transmission line such as an optical fiber cable and a coaxial cable. In this system, computers and terminals which are coupled to the plurality of stations communicate with each other through a looped transmission line. More specifically, for example, in order to transmit or send data from a terminal (T) 12.sub.1 connected to a station (STN) 10.sub.1 to a terminal 12.sub.n connected to a station 10.sub.n, data must be first transmitted from the terminal 12.sub.1 to the station 10.sub.1 and finally from the station 10.sub.n to the terminal 12.sub.n, as shown in FIG. 1. Data transmissions between the terminal 12.sub.1 and the station 10.sub.1, between the station 10.sub.1 and the station 10.sub.n and between the station 10.sub.n and the terminal 12.sub.n are performed in the same manner (according to data transmission procedures), as shown in FIG. 1. Reference numeral 101 denotes a send request signal; 102, a transmission permission signal indicating permission to transmit in response to the send request signal 101; 103, a signal comprising message data; 104, a transmission end signal indicating the end of transmission; and 105, a reception end signal indicating permission to terminate reception in response to the transmission end signal 104. In the above case where data is transmitted from the terminal 12.sub.1 to the terminal 12.sub.n, status data indicating that the data transmitted from the station 10.sub.1 has reached the station 10.sub.n must be sent from the station 10.sub.1 to tne terminal 12.sub.1. This status data must be transmitted in the same manner as a sequence of data transmission procedures involving exchange of signals (or data) 101 through 105 between the station 10.sub.1 and the terminal 12.sub.1, as indicated in the lower part of FIG. 1. FIG. 2 is a timing chart of the sequence of data transmission procedures as a function of time (plotted along the abscissa). Therefore, the following procedures are conventionally performed on a time serial basis:
(i) The send request signal 101 is transmitted from the terminal 12.sub.1 to the station 10.sub.1.
(ii) The transmission permission signal 102 is transmitted from the station 10.sub.1 to the terminal 12.sub.1.
(iii) The message data 103 and the transmission end signal 104 are transmitted from the terminal 12.sub.1 to the station 10.sub.1.
(iv) The reception end signal 105 indicating a permission to terminate reception in response to the transmission end signal 104 is transmitted from the station 10.sub.1 to the terminal 12.sub.1.
(v) The message data 103 is transmitted from the station 10.sub.1 to the station 10.sub.n.
(vi) The send request signal 101 is transmitted from the station 10.sub.n to the terminal 12.sub.n.
(vii) The transmission permission signal 102 indicating a permission to transmit in response to the send request signal 101 is transmitted from the terminal 12.sub.n to the station 10.sub.n.
(viii) The message data 103 and the transmission end signal 104 are transmitted from the station 10.sub.n to the terminal 12.sub.n.
(ix) The reception end signal 105 indicating a permission to terminate reception in response to the transmission end signal 104 is transmitted from the terminal 12.sub.n to the station 10.sub.n.
In the conventional data transmission system described above, in order to transmit data from a terminal connected to one (given) station to a terminal connected to another station, many data transmission procedures between the given station and the terminal of the station which is distant with respect to the given station must be performed. As a result, high-speed transmission cannot be performed. In such a system, a sequence of data transmission procedures are first performed between the given terminal and the given station. Thereafter, the data is transmitted from the given station to the distant station. The data is then further transmitted to the distant terminal only after another series of data transmission procedures are performed between the distant station and the distant terminal. As a result, high-speed transmission is difficult to perform.